This invention relates generally to the field of data communications networks and more particularly to an infrared communications network in which groups of personal computers and peripherals may communicate by infrared signals with each other and with other associated peripheral devices.
Personal computers have become widely used, creating a need to connect many such computers to each other or to a wide variety of peripherals. Typically, computers are connected to peripherals or other computers by hard wire. However, low cost cable communications interfaces (i.e. parallel printer ports or RS-232 serial ports) are limited in the distance they can reliably transfer data. Moreover, coaxial cable, which is used for considerably longer distance hard wire communications, requires a relatively expensive terminal interface and therefore isn't widely used for connecting peripheral devices to computers. As a result, peripheral devices in general must be co-located with a host computer. In addition, when using a hard wired approach to connecting terminals moving a terminal usually involves costly office building rewiring if the cables are installed properly to meet required electrical and fire safety standards.
Many users of computers need the capability to connect to several peripheral devices (e.g., disk memory, monitors, plotters, printers, modems, etc.), although not simultaneously. For example, a low quality printer (e.g., dot matrix) may be used for draft copies of word processing documents, while a higher grade letter quality printer may be used for the final copy. Also, relatively high cost, high quality, computer printing devices (e.g. laser printers) may only be cost effectively utilized if many computers or word processing terminals are able to share them. This need to share peripherals creates an additional problem by requiring the users to insert additional devices between multiple computers and the shared peripheral(s). The prior art hard wire solution to this problem of sharing peripherals has been to used manually operated selector switches, patch panels, or to simply manually make the cable connection as needed. However, while manually switching solves the connection problem, the greater problem of flow control (i.e. sending data only after a correct connection has been established) also must be manually supervised. Manual flow control supervision is difficult and susceptible to error, therefore results in lost transmissions if shared peripheral devices are not located conveniently in the same room as the computer that shares them. Thus, multiple cable hard wired systems are limited in that they are expensive to install and if not enclosed create safety hazards and aesthetic clutter. In addition each device must be physically, individually wired, each interface must match mechanically and electrically, and each path is dedicated and thus has limited, if any, multiple access to all of the installed functions.
Non-hard wired, one-way data communication systems which employ modulated infrared or radio frequency signals to transfer information are not unknown in the art. Radio frequency systems create serious problems due to interference and the need for relatively wide band-width as well as governmental licensing and regulation problems. One-way infrared systems exist in the prior art using modulated infrared signaling, for example, television remote control devices and wireless stereo headphones. However, the techniques used in such one-way systems are not suitable for the high level (i.e. 100%) end-to-end transmission accuracy required for communications between computer systems and peripheral devices.
Some two way infrared communication systems are known in which all terminals are synchronized to a host computer. One two-way system known in the art comprises the plurality of satellite stations used to cover an extended area. However, this system is limited in that it uses separate down-link and up-link subcarriers and requires centralized control of the system for proper operation of terminals. This system is primarily suitable to terminal to host computer communications and not for terminal to terminal communications.
Whether a one way or two way system is used, prior art systems are additionally limited in that beam blockage creates lack of adequate up time reliability and increases the error rate. In addition, these systems are limited in range (some are well under 50 feet). Also, prior art systems lack data security allowing any receiving device within range to intercept data transmissions.
Accordingly, it is an object of this invention to provide a novel low cost infrared communications network which enables two-way error free transfer of data between terminals while accommodating breaks in the direct optical path.
It is another object of the invention to provide a novel infrared communication system utilizing a packet switching protocol, which allows any terminal to select communications with any other terminal or terminals without degrading the error rate.
It is yet another object of the invention to provide a novel infrared communication system which employs a packet switching protocol permitting any terminal to function as a store and forward repeater.
Briefly, according to one embodiment of the invention a novel communication system is provided using infrared signals to provide two-way error free transfer of data between a plurality of computers or terminals.